Mammalian brain is a complex, intricately organized organ responsible for information processing, cognition and behavioural responses to environmental challenges. Currently two major classes of methodological approaches, such as electrophysiology and imaging/microscopy are used to study brain function and pathology in mammals. Electrophysiological methods range from activity registration of cell ensembles either by electroencephalography (EEG) or by means of implanted electrodes and multielectrode arrays to single cell recordings by means of patch clamp technique, for example. Imaging and microscopy methods employ in turn a variety of electromagnetic radiation spectral segments, such as visible or infrared light, X-rays, microwaves, magnetic resonance and the like. For those skilled in art it is clear, that the most common object for conducting laboratory scale experiments on mammals is a small rodent, such as a mouse or a rat. Correspondingly a variety of experimental setup is developed mostly for small rodents. The terms ‘animal’, ‘experimental animal’, ‘small experimental animal’, ‘laboratory animal’ and the like refer in this disclosure to a small rodent, such as a mouse or a rat.
While low-resolution microscopic imaging and implanted electrode-based electrophysiology experiments are relatively easy to perform on awake and freely moving animal, both single cell recordings and high-resolution imaging experiments on awake and moving animal represent a significant challenge. In accordance with current practice the latter methods are performed either on anesthetized animals (Hofer et al., 2009; Holtmaat et al., 2009) or require utilization of highly specialized devices, such as implanted fiber optics or miniaturized microscope scanning heads (Flusberg et al., 2005; Flusberg et al., 2008). Several technical approaches are known to be available at present for in vivo two-photon microscopy (TPM) in brain tissue of small experimental animal. All these approaches are based on craniotomy (Holtmaat et al., 2009) and similar methods of head fixation under the microscope objective (Holtmaat et al., 2009; Yang et al., 2010). A majority of these approaches are performed on anesthetized animal, which consequently implies a presence of negative side effects from anaesthetics (Larsen and Langmoen, 1998). These side effects are mostly due to the prolonged exposure to anaesthetics or repeated administration of anaesthetics.
It is however clear for those skilled in art that the functionality of unconscious brain may not be considered a suitable object for modelling working brain activity (Nallasamy and Tsao, 2011). Whether anaesthetic agents are to induce changes in precise architecture of neuronal membrane lipid bilayer and act as allosteric inhibitors or activators for different receptors and channel proteins on cellular surface (Chau, 2010), cell physiology, in particular physiology of neurons, in regard to an animal exposed to any anaesthetics may not be considered comparable to that in regard to an animal provided with no anaesthetics.
However, one should face that performed on anesthetized animal repetitive imaging sessions, long imaging sessions or combinations thereof (Hofer et al., 2009; Holtmaat et al., 2009) are still considered as approaches providing at a time present best microscopic results in vivo, although these techniques bear all limitations disclosed above.
In addition to abovementioned physiological limitations caused by anaesthesia, several methodological techniques are known from prior art that are simply not applicable for unconscious animal for technical reasons. That refers, in particular, to classical behavioural paradigms, for example those, utilizing behavioural tasks for animals in a labyrinth. Studies of the kind utilize various cage-like devices adapted to induce specific behavioural responses in an experimental animal. U.S. Pat. No. 3,974,798 discloses a method and an apparatus in the form of cage for studying a behavioural response of an experimental animal to various natural and artificial stimuli, such as vibration of cage floor or conducting a current therethrough. U.S. Pat. No. 7,086,350 discloses an animal cage behaviour system for monitoring complex behaviours in small laboratory animals, such as rats, mice, rabbits, guinea pigs etc., by means of applying thereto widely known tests, such as certain feeding patterns or fluctuating dark-and-light cycles.
Conducting neurophysiological studies on awake and freely moving experimental animal, while obtaining a behavioural response, still represents a problem for scientific community. In other words, a problem still exists of combining advanced modern techniques as two-photon microscopy in brain tissue in combination with classic behavioural tests. Those skilled in art may credibly estimate the scale of abovementioned problem and understand grand importance thereof in modern brain research.
Certain systems exist, providing a partial solution to the abovementioned problem. One of the systems exploits an idea dated back to 1930-s and disclosed in U.S. Pat. No. 1,794,951 and provides a simple device representing a tread wheel on which experimental animal can move only straight forward or backward while its head is fixed under multiphoton microscope during imaging session (Wienisch, 2011). Another much more elegant and advanced system setup utilizes an idea of suspended in the air spherical treadmill (Hölscher et al., 2005), on which animal can walk in different directions while its head is fixed under two-photon microscope during imaging (Dombeck et al., 2007). Combination of spherical treadmill setup with virtual reality system enables tracking the path of an experimental animal and therefore approaches simple behavioural paradigms, such as T-maze (Kendler, 1947).
Above mentioned systems are constrained with several common problems. The first problem is the translation of results, obtained from animal experiments on a curved surface, onto classical behavioural paradigms that are largely based on a prerequisite of a flat surface imitating to some extent natural environmental conditions. The second problem originates from an unnaturally unlimited surface provided by both abovementioned systems (Wienisch, 2011, Hölscher et al., 2005). The problem therefore lies in a lack of sensory stimulating obstacles normally featured in classical behavioural paradigms as well as in natural environmental conditions. Moreover, one of the necessary requirements for realization of existing approaches is a complete reconstruction of a microscopic setup, since the height of mandatory equipment does not otherwise allow fitting abovementioned systems under the microscope. Such reconstruction may cause problems with optical path alignment and furthermore microscopic equipment is not necessarily longer serviced by microscope supplier. Considering the prices on advanced microscopic equipment, loss of supplier warranty may be an important factor preventing complete reinstallation of said equipment.
It is therefore desirable to provide a system and method for bridging a gap between neuronal activity- and behavioral research with relatively simple and accessible realization means.